Most commercial public wireless networks contain a significant amount of network infrastructure which allows mobile wireless devices (e.g., wireless telephones) to communicate with each other as well as with other networks (e.g., a wired telephone network). In such networks, the infrastructure, which includes components such as base stations and other network controllers, handles network control and routing operations. The locations of the network infrastructure components are fixed, and the locations of the various components are designed to provide a desired level of network performance. Thus, each wireless device communicates directly with fixed network infrastructure components.
In areas where there is little or no communication infrastructure, wireless devices may communicate with each other by organizing into an ad-hoc wireless network. Ad-hoc wireless networks have no central control, and each wireless device which is part of the network operates as an individual communications device as well as part of the network infrastructure. Thus, each wireless device may originate messages and receive messages, but each wireless device also functions to route messages between other wireless devices which may not be in direct communication with each other.
For example, a simple ad-hoc network is shown in FIG. 1. Consider three wireless devices A, B, and C. Terminal A's communication range is shown by circle 102, terminal B's communication range is shown by circle 104, and terminal C's communication range is shown by circle 106. Thus, terminals A and B can directly communicate with each other, and terminals B and C can directly communicate with each other, but terminals A and C cannot directly communicate with each other because they are outside of each other's range. Terminals A, B, and C may organize into an ad-hoc wireless network in order to allow all three terminals to communicate with each other. This would require that terminal B act as a router to relay message between terminals A and C. Of course, in practice, ad-hoc wireless networks would likely have more than three wireless devices, and as such, routing and communication between all devices becomes an interesting problem.
Ad-hoc networks do not rely on wireless network infrastructure for communication, but instead they rely on peer-to-peer interactions for network communication. There are many applications for ad-hoc wireless networks. For example, military personnel on the field of battle; emergency disaster relief personnel coordinating efforts where there is no wireless infrastructure; sensors embedded in physical structures, such as airplane wings, exchanging data on dynamic stresses; and informal educational/professional gatherings where participants wish to communicate with each other.
One of the main issues in setting up an ad-hoc wireless network is connectivity of the wireless devices. A goal of an ad-hoc wireless network is full connectivity, meaning that there exists at least one communication path between all wireless devices. Such a path may not be a direct path and may involve multiple relays or hops among intermediate terminals. One of the constraints in reaching full connectivity is the transmission power of the wireless devices. Full connectivity would be a trivial problem if all wireless devices could transmit at a power sufficient to connect to all other wireless devices. However, power is a limited resource, and power management is required in the wireless devices. Another problem with using high power is that wireless devices operating within transmission range of each other will interfere with each other's transmissions and the higher the transmission power the more severe the interference. Thus, the goal is to use the minimum power level (so as to reduce interference and power consumption) required for full connectivity.
Existing techniques for setting power level of wireless devices in an ad-hoc wireless network have generally been based on a common power level assumption. In such networks, all wireless devices transmit at a common power level. As such, these techniques are directed to determining the minimum common power level required to obtain full connectivity. One of the problems with a common power level system is that some of the wireless devices which organize in a cluster will operate at a power level which is higher than necessary for full connectivity. Such higher power level will result in inefficient power management as well as a high level of interference between the wireless devices which are located relatively close to each other within the cluster. Another problem with the common power technique is that it assumes global knowledge of the distances between nearby wireless devices. That is, some central processing unit must know of the range requirement for connectivity of each wireless device in order to calculate the minimum common power level for all wireless devices.